Role of Organic Geochemistry in Petroleum

Role of Organic Geo chemistry in crudeA review on role of total geochemistry in vegetable anointcharacterization and applications of different basinsHarish Chandra JoshiAbstractPetroleum is a mixture dominantly of hydrocarbons with varying proportions of non-hydrocarbon constituents and traces of organomet every last(predicate)ic compounds. Generally Petroleum has an average composition of 85% carbon, 13% hydrogen, and 2% of sulphur, due north and oxygen. The aim of study is to find out the physicochemical and genetic property of petroleum. In this study biomarkers, age specific biomarker and reservoir geochemistry can be apply for the characterization, correlation and/ or reconstruction of the depositional surroundings as micro and macro fossils used by the geochemist.Keywords Biomarker, transmissible Characterisation, Kerogen, Geochemical Fossils.IntroductionThe name geochemistry was first used by the Swiss chemist, Christian Friedrich Schonbein in 1838. Petroleum geochemis try is the application of chemical principles to the study of the origin, migration, accumulation, and alteration of Petroleum ( vegetable embrocate and gas) and the use of this knowledge in exploring and recovering Petroleum. Organic chemistry is the branch of chemistry that deals with the dissemination and composition of carbon compounds. Geochemistry is the study of the chemical composition of the earth, minerals, ores, flutters and also is the study of the origin of petroleum. The major tasks of geochemistry can be summarized as followsThe study of the relative and absolute abundances of the elements and of the atomic species (isotopes) in the earth.The study of the distribution and migration of individual elements in the various deducts of the earth (the hydrosphere, atmosphere and lithosphere etc.), and in mineral and flaps, with the object of discovering their distribution and migration.Exploration companies have used petroleum geochemistry in hydrocarbon exploration. Th e joltingly and major objective of exploration geochemistry, is to reduce the risk of drilling dry holes. Petroleum geochemistry is based on the radical origin of the oil and gas whereby innate matter obtained from dead plants and animals. Organic matter is converted to hydrocarbons in the subsurface through various major three stages of transformations diagenesis, catagenesis and metagenesis. German scientist Treibs (1936) reveal a relationship between chlorophyll-a in living photosynthetic organisms and porphyrins in Crudes of petroleum. This connect provides a strong evidence of organic originof Petroleum. From the starting of the Precambrian till the Devonian, the unique primary producer of the organic matter were marine phytoplanktons. Since the Devonian an increasing mensuration of primary production has been contributed by higher terrestrial plants. At present cenario marine phytoplankton and higher terrestrial ar estimated to produce about equal amounts of organic ca rbon. On increases the burial depth, porosity and permeability decrease, and temperature increases. Thus lead to the change a gradual halting of microbial activity and thus eventually called organic diagenesis to a halt. As the temperature rises, thermal reactions become increasingly. This second transformation phase, called catagenesis, during the catagenesis kerogen begins to decompose into smaller, more mobile grains. In the early stage of catagenesis, kerogens argon still comparatively large these ar precursors for petroleum and ar called bitumen. In the late stages and final transformation stage, called metagenesis. During metagenesis the principal products consist of smaller gas molecules. Further, kerogens create from different organic matter, or under different diagenetic conditions, argon chemically clear which has a significant effect on hydrocarbon generation.Characterization of crude oil by Analytical MethodsFirstly sampling of crude oils is required for their chara cterization. Oil should be collected as a single- phase sample under squash conditions as they argon in reservoir. Therefore for the geochemical studies, crude oil samples are collected at the well head under atmospheric pressure. Under these conditions unmortgaged hydrocarbons of crude oils are lost completely or partly. Light hydrocarbon fraction gives the ideas only about the abundance and constituents of the light end of the oil. It is normally observed that the most abundant feature films hydrocarbons are commonly in the light fraction. For required minimizing the effects of sampling error the crude oil is distilled at 2100C. The heavier fraction is considered the foremost part of the crude oil. It is used to describe the chemical composition of a crude oil and also to compare it with other crude oils.Analytical Techniques in Petroleum ExplorationPetroleum system (Demaison, 1994 Hunt, 1996) comprise all those geological elements and processes that are necessary for an oil an d gas deposit to occur in nature. These main elements are a petroleum writer rock, migration paths, reservoir rocks, seals, traps and the geological approach that design each of them. Such systems involve a genetic relationship between the source rock and the petroleum accumulations, but proof of that relation force a geochemical correlation. organic geochemistry techniques available include surface geochemical prospecting, source rock geochemistry, crude oil geochemistry, natural gas geochemistry, biomarker geochemistry, isotope geochemistry etc.Biomarkers in PetroleumBiological marker or shortened to Biomarkers (Seifert and Moldowan, 1981) are complex molecules derived from once living organisms they are establish in sediments and oil and show little change in structure from their parent molecules (Peters Moldowan, 1993 and Hunt, 1996). These compounds are also called as geochemical fossils (Eglinton and Cavin, 1967) because of their origin from living organisms. Such compounds may be derived from terrestrial (mostly plants, marine pelagic (mostly plankton) and marine benthonic (algae, bacteria and other microbes). Biomarkers are generally, microfossils less than 30 nm in diameter and are highly variable in their stereochemistry i.e. the spatial arrangement of atoms and groups in their molecules.The common use of the biomarkers in petroleum exploration may be enumerated as followsBiomarkers are present in both and oil a source rocks so they provide vital information for the oil-oil and oil-source correlation.Organic matter type (source of organic facies)Depositional environmentExtent of thermal maturationDegree of biodegradationInformation about the age of the source rock and Geometry of BiomarkersSteranes obtain from the diagenesis of natural products sterols. Diagenesis converts sterol via chemical dehydration and microbial reduction to a steranes cholestane. Cholestane molecule is drawn in three dimensions as follows. The hydrogen at the 3 position p oints up above the plane of the molecule and that at the 5 position points down below the plane (Peters and Moldowan 1993) habitually Used Biomarkers in Petroleum ExplorationNormal Alkanes Normal alkanes are a homologues series of saturated hydrocarbons of general formula CnH2n+2. All linear n-alkanes from C1 to C40 and a few beyond C40 derived from different sources have been identified in crude oils.Iso- and Anteiso-alkanes Isoalkanes are 2- methyl radical alkanes and quite a number of these have been observed in crude oils as have been the anteiso-alkanes, the 3-methlyalkanes. Iso and anteiso alkanes are associated with n-alkanes in plant waxes where they comprise a approximate number of carbon atoms (about 25-31) with an odd predominanceFigure 1. Showing common biomarkers like paraffins, Iso and ante-isoalkaneAcyclic Isoprenoid These are special type of Iso-alkanes in which one methyl group is attached to every fourth carbon atom in straight. Isoprene (methyl butadiene) is the b asic structural unit composed of carbon atoms that is found in all biomarkers. The most common isoprenoids are pristane (C19) and Phytane (C20).Figure 2. Common Isoprenoid biomarkers in petroleumTerpenoids Terpenoids can be classified based on structural types into diterpenoids and triterpenoids Diterpenoids are categorized into bicyclic and tricyclic diterpenoids. Triterpenoids are grouped into tetra and pentacyclic. The most knowing are pentacyclic and among these are hopanes. Hopanes are pentacyclic triterpenoids comprised of four 6-membered and one 5-membered ring. There is a side chain which can contain upto 8 carbon atoms. Thus the series comprise of C27-C35 hopanes. They are believed to have originated from polyhydroxybacteriohopane.Figure 3. Structures of Common TriterpanesFigure 4. Structures of Common Tricyclic and Tetracyclic TerpanesSteranes Steroids can be classified as aliphatic and aromatic steroids (mono, di- and tri-aromatic depending on the number of aromatic rings ). Steranes are a series of aliphatic steroids. The sterols in all eukaryotic organisms are precursors to the steranes in sediments and petroleum. Like the hopanes, steranes are abundant in sediments, rocks and petroleum, because their precursors (Sterols) are so common in living organisms. Cholesterol has octonary asymmetric centers and might be expected to show as many as 28 or 256 stereoisomers.Figure 5. Chemical Structure of various steroidsPorphyrins Porphyrins are characterized by a tetrapyrrolic nucleus proved to be inherited from chlorophyll, the green photosynthetic pigment of plants and animals ,hemin, the red pigment of animal blood. These tetrapyrrolic organometallic compounds reported of the vanadium and nickel in petroleum. The major types of fossil porphyrin are deoxophylloerytrapyrrole (DPEP) and etioporphyrin (ETIO) porphyrin structure.Age specific biomarkersIf biomarkers characterise a molecular record of life, they can be used for age determination. reliable ag e specific biomarkers like Oleanane present in oils derived from late Cretaceous or Younger. C11-C19 Paraffins, Odd carbon number prevalence in oil from many Ordovician sources. 24-n-propylcholestane, High in oils from Ordovician sources.Thus the biomarkers transport to the sources has proved to be of great help in geochemical characterization of the oils/condensates.Reservoir GeochemistryThe main aim of reservoir geochemistry is to understand the distribution and origin of the petroleum, water and minerals in the reservoir and account for their possible spatial and compositional variation (Cubitt and England 1995). A better understanding of the fluids in the reservoir make out to a better understanding in an area and prioritization of exploration thrusts. The principle factors responsible for difference in petroleum composition are the effect of organic facies variations, progressive source rock maturation, migration fractionation, gravity segregation, oil/water contact and non-un iform biodegradation of oil across the field. However these effects have been normalized by using ratios of peaks agree to compounds of similar molecular weight in the C10+ region of the chromatogram.The study of reservoir continuity is also the focus of the geochemical characterization to trace the nature and depositional conditions of the source organics, realisation of the oil families and thermal maturity of the oils/condensates.When a set of chromatographic peaks has been selected, a variety of techniques are available for grouping of this data. One way is to use a diametral plot of selected ratios by a star diagram (polygon plot) by plotting each peak ratio on a different axis of polar plot. Each data point is plotted from the centre of the concentric circles outward. The points are then connected to create a star shaped pattern characteristic of each oil.Applications of geochemical characterisationBiomarker and non-biomarker geochemical parameters are best used together to supply the most authentic geological interpretations to help solve exploration, enlargement, production and environmental problems. prior(prenominal) to biomarker work, oil and rock samples are properly screened using non biomarker analyses. The strength of biomarker parameters is that they provide more detailed information needed to answer questions about the source rock depositional environment, thermal maturity and the biodegradation of oils than non-biomarker analyses alone. Different depositional environments are characterized by different assemblages of organisms and biomarkers. Commonly accept classes of organisms include bacteria, algae, and higher plants. Biomarker parameters are also an effective means to take in the relative maturity of petroleum through the entire oil-generative window.ConclusionOn the basis of above observation major conclusions which have been derived from the whole study are as followsThe presence of complete range of normal alkanes upto nC36 and i n some cases upto nC40. The presence of biomarker in oil indicates that oil may be terrestrial or marine. The terrestrial nature of the source is also strongly indicated by the steranes. Reservoir geochemistry of oils has been used to demonstrate the lateral/vertical continuity/compartmentalization.ReferencesBhandari, A., Prasad, I.V.S.V., Kapoor, P.N., Varshney, Meenu, Madhavan, A.K.S., Pahari, S. and Singh, R.R., 2008. 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